Hives, or
"wheals", are pale red swellings of skin that occur in groups on any part of
the skin. Urticaria is the medical word for hives. Each hive lasts a few
hours before fading without a trace. New areas may develop as old areas
fade. They can vary in size from as small as a pencil eraser to as large as
a dinner plate and may join together to form larger swellings. Hives usually
are itchy, but may also burn or sting.

Hives are formed
by blood plasma leaking out of small blood vessels in the skin. This is
caused by the release of a chemical called histamine. Histamine is released
from cells called "mast cells" that lie along the blood vessels in the skin.
Allergic reactions, chemicals in foods, or medications can cause histamine
release. Sometimes it's impossible to find out why hives are forming.

Hives are very
common - 10-20 percent of the population will have at least one episode in
their lifetime. Most episodes of hives disappear quickly in a few days to a
few weeks. Occasionally, a person will continue to have hives for many
years.

Typical outbreak of urticaria

When hives form
around the eyes, lips, or genitals, the tissue may swell excessively.
Although frightening, the swelling usually goes away in less than 24 hours.
However, if you have difficulty breathing or swallowing you should go to the
emergency room.

Acute Urticaria
Hives lasting less than six weeks are called "acute urticaria." With this
type of hives, the cause can usually be found. The most common causes are
foods, drugs, or infections. Insect bites and internal disease may also be
responsible. Other causes can be pressure, cold, or sunlight.

Foods
The most common foods that cause hives are nuts, chocolate, fish, tomatoes,
eggs, fresh berries, and milk. Fresh foods cause hives more often than
cooked foods. Food additives and preservatives may also cause hives.

Hives may appear
within minutes or up to two hours after eating, depending on where the food
is absorbed in the digestive tract.

Drugs
Almost any prescription or over-the-counter medication can cause hives. Some
of those drugs include antibiotics, pain medications, sedatives,
tranquilizers, and diuretics (fluid pills). Diet supplements, antacids,
arthritis medication, vitamins, eye and eardrops, laxatives, vaginal
douches, or any other non-prescription item can be a potential cause of
hives. If you have an attack of hives, it's important to tell your doctor
about all of the preparations that you use to assist in finding the cause.

Drug-induced urticaria

Infections
Many infections can cause hives. This includes bacterial as well as fungal
infections. Colds are a common cause of hives in
children.

Systemic
fungal disease

Chronic
Urticaria
Hives lasting more than six weeks are called "chronic urticaria". The cause
of this type of hives is usually much more difficult to identify than that
of acute urticaria. In patients with chronic urticaria, the cause is found
in only a small number of patients. Your doctor will need to ask many
questions in an attempt to find the possible cause. Since there are no
specific tests for hives, testing will depend on your medical history and a
thorough examination by your dermatologist.

Physical
Urticarias
Hives can be caused by sunlight, heat, cold, pressure, vibration, or
exercise. Hives due to sunlight are called solar urticaria. This is a rare
disorder in which hives form on exposed areas within minutes of sun exposure
and fade within one to two hours. Hives due to the cold are more common.
These appear when the skin is warmed after exposure to cold. If the cold has
affected large areas of the body, large amounts of histamine may be released
which can produce wheezing, flushing, generalized hives, and fainting.

Dermatographic
Urticaria
Hives that form after firmly stroking or scratching the skin are called "dermatographism".
It affects about 5 percent of the population. Most people with this
condition are otherwise healthy. These hives can also occur along with other
forms of urticaria. They may typically appear in young women and last for
months or even years.

Dermatographism

Treatment
The best treatment for hives is to find and remove the cause. This is not an
easy task and often not possible. Antihistamines are usually prescribed by
your dermatologist to provide relief. Antihistamines work best if taken on a
regular schedule to prevent hives from forming. No one antihistamine works
best for everyone, so your dermatologist may need to try more than one or
different combinations to find what works best for you. In severe hives, an
injection of epinephrine (adrenalin) or a cortisone medication may be
needed.